Three separate but linked customary practices are concerned with the exchange of money between individuals. At least from the medieval period onwards, the handing over of ‘God's penny’ (which could be any amount above a penny) was one of the ways in which two traders sealed a bargain, and was thus the equivalent to a binding deposit given by the buyer. The name possibly derives from an earlier belief that this sum should be given to the Church as a voluntary donation. ‘Earnest money’ was usually a sum given to a new servant or farmworker on being hired by a new employer. Having accepted the earnest, the employee was bound to turn up for work at the agreed date. The same principle applied to the King's Shilling given to a new recruit to enlist him into the army. However, as the name implies, ‘earnest money’ (i.e. the concept of a promise) could be used to apply to the buying of goods or to the securing of staff, so the terminology can be confusing (see, for example, Thomas Dekker's The Shoemaker's Holiday (1599), iii. 1). There were a number of local terms for earnest money, including Arles or Erles in the northern countries and Fasten or Festing money elsewhere.
Luck money was something different. This was a sum of money given back by the seller, to the buyer, on the completion of a deal, for luck. Hard-fought attempts by farmers and manufacturers to eradicate the practice which are reported throughout the 19th century showed how prevalent and ingrained the custom was. Numerous reports also indicate that it was necessary to spit on the money if you wanted its luck to be effective, and this custom was still being reported in certain quarters late in the 20th century.
F. J. Snell, The Customs of Old England (1911), 232–8;N&Q 5s: 7 (1877), 488;5s:8 (1878), 37–8 376–7;9s:11 (1903), 127, 196, 254, 358;157 (1929), 454–5;158 (1930), 31;Opie and Tatem, 1989: 233–4.